Many expressed frustration about the outage, saying there was no warning despite the fact there was an hour gap between the time a generator went offline and the rolling outages began.

According to a spokesperson with the California ISO, a generator stopped working at 11:53 a.m. on Sunday. Spokesperson Steven Greenlee said that caused transmission lines to become overloaded and “threatened to spread to other facilities.”

Around 1 p.m., the ISO ordered power lines in San Diego to be shut off. They ordered a reduction of 150 megawatts. 1 megawatt powers about 650 homes, according to Greenlee.

Greenlee said during the hour from the breakdown of the generator to the outages, they were working to stabilize the system, hoping to avoid any disruption in service.

Representatives with both the ISO and SDG&E said there were no email alerts because they did not anticipate the outage.

Greenlee likened the grid to a car breaking down, saying the grid is a “big machine.”

“Things happen on it and electricity is very fickle, so whenever that voltage starts going astray, we often 99 percent of the time are able to correct it,” Greenlee told Team 10 over the phone.

He said when the generator went offline, it started “messing with the voltages in the area.”

When asked how the agencies pick what neighborhoods to shut down electricity, Greenlee directed Team 10 to SDG&E.

Hana Eisenman, a SDG&E media representative, said the outage areas were spread out by design. Engineers are the ones in charge of figuring out which areas are affected. They select those areas based on the most efficient way to deal with the outage and reduce impact to customers, Eisenman said.

He said for unexpected outages, like the one San Diegans experienced on Sunday, there is not a city-by-city list the utility company goes by.